Fibrous composition boards have been used for years in interior ceilings and other interior walls of buildings to provide exposed surfaces which are ornamental or decorative and which preferably also function to improve the acoustical properties of the walls. It has been a popular practice to form perforations, fissures, cavities, and other forms of openings of various types and shapes, on the surface of the board to be exposed to impart improved aesthetic and acoustical properties to the boards.
These openings typically have been formed by mechanically drilling, punching, piercing or die-forming the dry board stock produced by drying the wet lap. In some cases the surface of the dried board has been brushed or abraded or eroded by sandblasting to impart a roughened texture to portions of the visible surface in attempts to provide additional or different aesthetic effects. Before drying, however, the wet lap has very little strength. While some types of surface texturing and fissuring have been performed on the wet lap before drying it, as by dragging the surface of mineral fiber wet lap board stock with a screed or drag bar to form fissures in it, the type and amount of working of the surface prior to drying of the wet lap are limited by the lack of strength of the wet lap and by other properties and characteristics of the wet lap.
The walls or boundaries of the fissures or textural contours are usually more cleanly defined if they are produced in the surface of the board after it has been dried, rather than before, and because this clean definition has been favorably regarded, much emphasis has been placed on the techniques of treating the surface of the dry board. This procedure has some disadvantages, however, such as a tendency to weaken the board by severing or tearing the fiber network after the board has been dried or set. Thus, in spite of the keen competition and incentive in the trade to produce boards with new and superior aesthetic effects and with at least adequate acoustical and other properties, success has been limited. Only a relatively few basic practical techniques for surface treatment, to open or contour the surface of the boards, have been found feasible or commercially attractive, and this has limited the ornamental effects achieved.
In this situation, it has become increasingly desirable but difficult to achieve any strikingly different and pleasing departure from the old aesthetic concepts in these ornamental fibrous boards in which the ornamentation is provided chiefly by opening the surface of the board. It has been particularly difficult to find a commercially practicable process which provides a new aesthetic effect along with the acoustical and other utilitarian characteristics desired of such boards.